Lecture 1 Flashcards
What is the purpose of the cell membrane and what are its constituents?
It is to separate the IC fluid from the EC. It is made from 55% protein, 42% lipid and 3% carbohydrates
Name the relative concentrations of sodium, potassium, calcium, chloride, proteins, anions, phosphate and bicarbonate inside and outside the cell
1) sodium high EC, low IC
2) potassium low EC, high IC
3) calcium lowEC, very low IC
4) chloride high EC, low IC
5) anions high EC
6) phosphates high IC
7) bicarbonate high EC and blood plasma
8) proteins high plasma, very high IC
How do different types of particles travel through the membrane?
1) lipid soluble= diffuse through the membrane
2) small molecules and ions= protein transporters
3) large molecules= endocytosis
Name 3 types of protein transporters
1) ion channels= selective pore that opens and closes. Passive transporter
2) carriers= facilitated transport proteins , passive transporter (doesn’t directly use ATP)
3) Pumps= require the presence and hydrolysis of ATP to move ions against their electrochemical gradient
Name the properties and function of sodium potassium ATPase
1) is ubiquitous= found everywhere except dog RBC
2) generates a net charge of -1
3) keeps IC sodium low- if it stops working so does the rest of the cell
4) is a tetramer= 2 alpha subunits and 2 beta
How do carriers function?
Carriers transport ions and small molecules across their electrochemical gradient with a turnover of 10^2 to 10^3. They become saturated when all are occupied. Carrier mediated diffusion is much faster than diffusion. They don’t actively use ATP but rely on its use for exchangers e.g. sodium glucose transporter
what are the 3 types of transporters?
Uniporter, symporter (co-transport) and antiporter
What are the properties and functions of ion channels?
When open, they generate a current from the ions travelling along their electrochemical gradient. When closed there is no current generated. Some are non-selective. They have a turnover of 10^6 to 10^8 ions per second.
Describe how the patch clamp technique is carried out
1) The membrane potential is measured and a glass recording pipette makes contact with the cell membrane and suction creates a seal so that ions only flow through the pipette
2) the other electrode is sitting in another solution to compare the 2 solutions
3) a chloride wire is used as an ultrasensitive amplifier
What is the difference between macroscopic and microscopic currents?
Microscopic is the current through a single channel, macro is through many channels
How can the patch clamp technique be used experimentally?
To compare WT and mutant channels and to measure the change in current across the whole membrane by removing a section of the cell membrane allowing the pipette to be submerged in IC fluid
What is the total current equation? and what is G?
I= N0 x g x P ( Vm- Em). G is single channel conductance
Describe the properties of potassium channels
Require 4 subunits that come together to form a pore in the middle, allowing more than one K+ in at any one time. It is tested by x-ray diffraction- KcSA (bacteria homologue to kir) was crystallised and diffracted
